In a ferromagnetic memory cell, in which the storage medium is a stick or rod normal to the plane of the substrate, the static magnetic moment, or polarity, of the storage medium must be sampled to determine in which of two directions, north or south, the magnetic field is aligned at sense, or read time. Depending on the polarity of the storage medium, a binary value of “zero” or “one” is read. However, in accomplishing this sampling or sensing, consideration must also be given to the amount of area required by the sensing means. For example, in a matrix of memory cells, in order to accomplish high-density, it is important to reduce the area, or “real estate” required for data sense circuitry, as well as increase data acquisition speed, and lower power requirements.
Examples of patents related to non-volatile ferromagnetic memory cells, each of which are herein incorporated by reference for their supporting teachings, are as follows:
U.S. Pat. No. 4,360,899 to Dimyan et al. teaches a non-volatile random access memory having a plurality of magnetic cells arranged in an array on a major surface of a substrate. In operation, a single magnetic cell is selected and inductively switched between opposite remnant, (i.e. permanent) states, upon the simultaneous application of electrical pulses has an amplitude which is insufficient to inductively switch the remnant state of the selected cell. However, the combined amplitude of the electrical pulses is at least equal to the amplitude required for such a switch.
U.S. Pat. No. 5,068,826 to Mathews teaches a non-volatile, status magnetic memory device, whose operation is based on the Hall effect. The device includes a magnetic patch which stores data in the form of a magnetic field, a semiconductor Hall bar, and a pair of integrally-informed bipolar transistors which are used for amplifying and buffering the Hall voltage produced along the Hall bar in use, current is forced to flow down the length of the Hall bar causing the Hall voltage to be developed in a direction transverse to the direction of both the magnetic field and the current. The bases of the bipolar transistors are ohmically coupled to the Hall bar to sense the Hall voltage—the polarity of which is representative of the stores information. Finally, a system of current carrying conductors is employed for writing data to individual magnetic patches.
U.S. Pat. No. 5,295,097 to Lienau teaches a nonvolatile random access memory having a substrate that carried separate magnetically polarizable domains. Each domain is surrounded by a full write loop member, and arranged to penetrate a Hall channel of a dual drain FET with its residual magnetic field. The domains are organized in word rows and bit columns, are each written to by a single full write current through the surrounding loop member, and each read by a comparator connected to the FET drains. Independent separate write lines and read lines are used in writing and reading the values of each magnetic bit.
U.S. Pat. No. 4,791,604 to Lienau et al. teaches a sheet random access memory (SHRAM). The SHRAM is a nonvolatile and transportable memory characterized by its cell density and relatively small size and power requirements, but having the nonvolatile character and rugged transportability of core memory, or magnetic disks or tape. The SHRAM is further characterized by a memory comprising a two dimensional magnetic substrate and a fixed driving device for writing and reading into the substrate. Further, a fixed sensing device for sensing the information is attached at each cell location. The memory media includes not only a homogeneous two dimensional substrate, but also ferrite cores formed into the substrate by photolithographic techniques, wherein the information is stores within the cores and read by the sensing device from a gap defined by the core. Memory cells according to the invention can thus be arranged and organized to form destructive readout RAMs, or non-destructive readout Rams, in both serial and parallel form.
U.S. Pat. No. 5,926,414 to McDowell et al. teaches a magnetic integrated circuit structure in combination with a carrier-deflection-type magnetic field sensor. Each of a variety of magnet structures realize a condition in which the magnetic field is substantially orthogonal to the direction of travel of carriers of a sense current, thereby achieving maximum sensitivity. By basing a magnetic memory cell on a single minimum size MOS device, a small cell may be realized that compares favorably with a conventional DRAM of FLASH memory cell. The greater degree of control over the magnetic field afforded by the magnetic structures enables the cross-coupling between cells in a memory array to be minimized.
U.S. Pat. No. 3,727,199 to Lekven teaches a magnet memory element and a process for producing such elements in plurality to constitute a static magnetic memory or digital information storage system. Individual binary storage members are afforded directionally preferential magnetic characteristics by flux circuits to establish the preferred axis of magnetization. Conductors for driving the individual binary storage members (for storing and sensing) are provided in an organized pattern to accomplish selectivity. A batch production process is also disclosed.
To date, there have been no commercial examples of non-volatile ferromagnetic memories, capable of both random write and random read, with truly simple data sense circuitry.